For mammalian cells to survive, they must be able to respond rapidly to changes in their environment. Furthermore, for cells to reproduce and carry out other cooperative functions, they must be able to communicate efficiently with each other. Cells most frequently adapt to their environment and communicate with one another by means of chemical signals. An important feature of these signaling mechanisms is that in almost all cases a cell is able to detect a chemical signal without it being necessary for the chemical messenger itself to enter the cell. This permits the cell to maintain the homeostasis of its internal environment, thereby permitting the cell to respond to its external environment without being adversely effected by it.
These sensing functions are carried out by a variety of receptors, which are dispersed on the outer surface of the cell and function as molecular antennae. These receptors detect an incoming messenger and activate a signal pathway that ultimately regulates a cellular process such as secretion, contraction, metabolism or growth. In the cell's cellular plasma membrane, transduction mechanisms translate external signals into internal signals, which are then carried throughout the interior of the cell by chemicals known as "second messengers."
In molecular terms, the process depends on a series of proteins within the cellular plasma membrane, each of which transmits information by inducing a conformational change in the protein next in line. At some point, the information is assigned to small molecules or even to ions within the cell's cytoplasm, which serve as the above-mentioned second messengers. The diffusion of the second messengers enables a signal to propagate rapidly throughout the cell.
Several major signal pathways are now known, but two seem to be of primary importance. One employs cyclic nucleotides as second messengers. These cyclic nucleotides activate a number of proteins inside the cell, which then cause a specific cellular response. The other major pathway employs a combination of second messengers that includes calcium ions as well as two substances whose origin is remarkable: myo-inositol-1,4,5-trisphosphate (IP.sub.3) and diacylglycerol (DG). These compounds are cannibalized from the plasma membrane itself, by enzymes which are activated by specific cellular membrane receptors. However, it should be noted that myo-inositol in its non-phosphorylated form first must be synthesized by the cell from glucose or be obtained from the extracellular environment. The structural formula of myo-inositol is shown below: ##STR1## wherein the term "myo" refers to the stereochemical configuration of the inositol molecules. Since all known inositol second messengers use the D-myo-configuration of inositol, the term "inositol" will herein be understood to refer to D-myo-inositol. To form IP.sub.3, a receptor molecule on the surface of the cellular plasma membrane transmits information through the cellular plasma membrane and into the cell by means of a family of G proteins, which are cellular plasma membrane proteins that cannot be active unless they bind to guanosine triphosphate (GTP). The G proteins activate the so-called "amplifier" enzyme phospholipase C, which is on the inner surface of the cellular plasma membrane. Phospholipase C cleaves the cellular plasma membrane lipid, phosphatidylinositol-4,5-bisphosphate (PIP.sub.2) into DG and IP.sub.3. IP.sub.3 is a water-soluble molecule, and therefore, upon being released from the inner surface of the cellular plasma membrane, it rapidly diffuses into the cytoplasm. IP.sub.3 then releases calcium ions (Ca.sup.2+) from non-mitochondrial stores, to increase the cytoplasmic free Ca.sup.2+ concentration. DG is an activator of protein kinase C. See U. Kikkawa et al., Ann. Rev. Cell Biol., 2, 149 (1986). Taken together, the increase in cytoplasmic free Ca.sup.2+ concentration and the increased activity of protein kinase C leads to a sequence of events that culminates in DNA synthesis and cell proliferation (See M. Whitman et al., Biochim. Biophys. Acta, 948, 327 (1988)). Other inositol phosphates, in addition to IP.sub.3, are formed in the cell. For example, phosphorylation of IP.sub.3 by a specific 3-kinase gives inositol-1,3,4,5-tetrakisphosphate (IP.sub.4) (R. F. Irvine et al., Nature, 320, 631 (1986)), which may act synergistically with IP.sub.3 in the activation of Ca.sup.2+ -mediated responses in several systems.
Recently, another phosphatidylinositol signalling pathway has been identified and linked to the action of some growth factors and oncogenes. Phosphatidylinositol-3'-kinase (also designated type 1 phosphatidylinositol kinase) is found associated with a number of protein tyrosine kinases including the ligand-activated receptors for insulin, platelet derived growth factor (PDGF), epidermal growth factor (EGF), and colony-stimulating factor-1 (CSF-1) as well as protooncogene and oncogene tyrosine kinases (Y. Fukui et al., Oncogene Res., 4, 283 (1989)). This enzyme phosphorylates the D-3 position of the myo-inositol ring of phosphatidylinositols to give a class of phosphatidylinositol-3'-phosphates that are not substrates for hydrolysis by phosphatidylinositol phospholipase C and, therefore, appear to exert their signalling action independently of the inositol phosphate pathway.
Subsequently, DG and IP.sub.3 are recycled. DG is recycled by a series of chemical reactions which constitute one component of the lipid cycle, and IP.sub.3 is recycled by a series of reactions known as the phosphatidylinositol cycle. The two cycles converge at the point when inositol is chemically linked to DG. The DG-bound inositol is phosphorylated in a series of steps which ultimately results in the reformation of phosphatidylinositol diphosphate.
Previously, A. P. Kozikowski (U.S. Pat. No. 5,053,399) disclosed the synthesis of a number of D-3-deoxy-3-substituted-myo-inositols, in the expectation that these compounds would act as antimetabolites of myo-inositol-derived second messengers. In theory, such myo-inositol isosteres could act either by blocking the formation of certain phosphatidylinositols and inositol phosphates or by forming fraudulent analogs thereof. In fact, certain of these analogs, such as 3-deoxy-3-fluoro-myo-inositol, were found to exhibit cell growth inhibitory activities against normal NIH 3T3 cells in culture and several oncogene transformed NIH 3T3 cell lines. However, the D-3-deoxy-3-substituted-myo-inositol analogs were only effective inhibitors of cell growth in the absence of myo-inositol. In the presence of physiological concentrations of myo-inositol in the growth medium, the growth inhibitory effect of the analogs was antagonized. It is believed that myo-inositol effectively competes with the D-3-deoxy-3-substituted myo-inositol analogs either for uptake into the cell and/or for incorporation by the cell to phosphatidylinositols.
Therefore, a continuing need exists for analogs of phosphatidylinositol which are effective to inhibit the phosphatidylinositol cycle in a cell, e.g., to block cell growth, preferably to inhibit or prevent the growth of neoplastic cells and/or neoplastic transformation.